Conventionally, various problems caused by wild animals, such as damage on farm products due to the intrusion of animals into agricultural lands, accident due to the intrusion of animals into roads and railroads, damage due to the intrusion of animals into residence, damage such as bite damage on electric cables and communication cable networks and the like, accident by collision of bird with airplane and the like, are producing loss in life and loss in economy.
As a countermeasure for such damages caused by animals, various repellents are disclosed (patent documents 1, 2 and 3). Many of these repellents take note of odorants. However, since such repellents simply have an odor that the animals hate, they are considered to lose effect by habituation.
On the other hand, it is empirically known that an odor developed from excretion, secretion and the like of carnivorous animals induces an avoidance behavior of animals. Taking note of this effect, methods using the excretion itself of carnivorous animals as an animal repellent have been proposed and, for example, a product using urine itself of gray wolf (Canis lupus) as a repellent has been imported and sold. However, it is not easy to produce a large amount of the excretion of endangered animals such as wolf and the like.
An example of a specified odorant molecule inducing an avoidance behavior is 2,4,5-trimethyl-3-thiazoline (TMT). TMT was separated and identified as a component inducing a fear response, from the odor components secreted from the anal gland of fox, which is a natural enemy of rodent animals such as mouse, rat and the like. E. Vernet-Maury et al. analyzed the odor components contained in the feces of fox, and analyzed 70 kinds of odorant molecules for the effect on animals. As a result, an odorant molecule having the strongest effect was TMT (non-patent document 1).
Furthermore, Maury et al. analyzed the effect of 11 kinds of odorant molecules having chemical structures similar to that of TMT. However, their effects were equal to or less than that of TMT (non-patent document 2).
Based on these experimental results, TMT has been widely studied as a sole substance that induces fear in animals and shows a repellent action. However, its action is not clear, and induces only a weak response as compared to the odor of a natural enemy itself. Therefrom a question has been raised if TMT does not induce a fear reaction to a natural enemy but is simply recognized as a bad smell (non-patent documents 3 and 4). Alternatively, it is considered that the odor of natural enemy itself contains a mixture of odors of many compounds and a single compound cannot reproduce the effect.
Using the genetic engineering, the present inventors generated a neural circuit-modified mouse by intentionally removing a part of the olfactory neural circuit that processes the odor information, and conducted a unique study by analyzing the behaviors of the mutant mouse that smelled the odor, whereby to elucidate the biological function of individual olfactory neural circuits. As a result, they have clarified for the first time in the world that a fear reaction of a mouse to a natural enemy odor and an aversive response to a putrid odor are respectively and innately controlled by the olfactory neural circuit present in a particular intracerebral area (non-patent documents 5 and 6).
Therefrom it has been elucidated that TMT is a substance that induces fear in animals. However, TMT still shows a lower repellent effect as compared to that provided by the odor of a natural enemy itself, and a single substance having a repellent effect exceeding that of TMT has not been found as yet.